In the prior art, a plurality of motors are often operated using an individual converter which controls or regulates, for example, the torque, the speed or the position of the respective motor. This can be the case, in particular, when the respective motors do not have to be operated at the same time. In other cases, it may even be advantageous if the respective motors cannot be operated at the same time. According to one example, drives of machines having positioning axes are not intended to be moved at the same time as motors for protective doors or tool changers.
In order to individually electrically connect or disconnect the motors to or from the converter, electromechanical relays having individual contacts for each motor phase are used, for example.
However, electromechanical relays may be expensive and have a large construction volume. In addition, the mechanical contacts may wear out with increasing operating time. In the case of switching operations with high currents, there is also the risk of the electrical contacts being welded.
Electronic switches, which can also be referred to as semiconductor switches or solid-state relays, have the advantage that they do not have any mechanical switching contacts and can therefore be switched in a bounce-free and wear-free manner.
A switch for electrically connecting and disconnecting a motor must generally be designed to safely disconnect the current flow. Field-effect transistors (FET), for example, can be used as semiconductor switches. FETs block the current in one current direction and are still conductive in the other current direction even in their off state. In order to disconnect or block a current in both directions, two FETs are connected in series in the prior art and are arranged in such a manner that the first FET blocks the current flow in one direction and the second FET blocks the current flow in the respective other direction. This is often referred to as a “back-to-back” arrangement.
On the one hand, this results in a large design and a high outlay for the circuit. On the other hand, additional electrical losses occur since the current must flow through two semiconductor switches.